I've been having suicidal thoughts as of late also and I'm very glad that you shared your story here. I'm just at the beginning of my treatment for long-lasting depression and anxiety, but I think I have something figured out already and that might explain your situation to some extent.

We live our lives in bubbles. And that's okay. We aren't aware of our own mental defences, because if we were life would be very complicated. This is how most people live their lives: moderately happy in their moderate bubbles. It's not perfect, but it's better than acknowledging your weaknesses (and there's plenty).

It's just that sometimes these defences come down. Might it be for a bad break-up or a lost close one, bad drug experience even, it tears your world down. Maybe for the first time in your life you are forced to see how cruel and arbitrary world might seem if you just look it from another perspective. Sometimes this way of looking at the world stays on, and one needs to go to therapy, or has to keep on taking drugs to fight the misery, and sometimes it heals itself.

Nonetheless, if you feel you've reached your happy bubble again, it's important not to forgeg this feeling of anxiety you had. That is how few people feel constantly, and if you start to suffer from those feelings in the future it is important to acknowledge them honestly. Hope you happy living!